The present invention relates to reduction of noise levels associated with exhausting air from devices employing blowers or fans, and in particular to a muffler adapted for use with vacuum sweepers, floor scrubbers, carpet maintenance equipment, blowers and the like.
Appliances utilizing high speed fans to move air, such for example as vacuum cleaners and blowers, typically produce high frequency sounds emanating from the air exhaust outlet and attending the passage of air through the fan chamber. Ordinarily, given the same sound pressure level, high frequency sounds are more annoying than low frequency sounds.
Noise levels can be reduced by installing equipment such as dampeners or mufflers at the exhaust outlet from the air motor. The exhaust outlet of a vacuum cleaner, employing a fan system through which passes debris entrained in air, is provided with an enclosure to capture the debris. The enclosure is usually made of a porous material and called a filter bag, so that air entering the enclosure may pass therethrough while debris is contained. When the filter bag is mounted in a location above the air motor, as for example in upright and external canister vacuum cleaners, it contains a tubular sleeve which attaches to the vacuum cleaner exhaust outlet. The function of the sleeve is to act as a stand pipe to keep the bag inlet above collected debris, so that debris does not choke off the inlet to the bag before the bag is full.
Conventional filter bags do little to reduce high frequency noises attending the passage of air at high velocity. The art therefore contemplates various muffling techniques to reduce the level of such noises, and in U.S. Pat. No. 2,130,495 a muffler for a vacuum cleaner extends from the exhaust outlet to an upper portion of a filter bag and comprises inner and outer tubular cloth sleeves having a tubular felt sleeve therebetween. In U.S. Pat. No. 2,287,867 a muffler for a vacuum cleaner comprises a short tubular section of sponge rubber positioned between the exhaust outlet and an inlet to a filter bag, and U.S. Pat. No. 4,015,683 teaches a somewhat similar foam material muffler, except that the flow path through the muffler comprises a central passageway having a plurality of radially extending grooves. In all of the aforementioned mufflers, the cellular texture of the muffler surface has the property of absorbing some volume of the noises in the air, and to that extent contributes to a greater quietness of operation. However, a disadvantage of such mufflers is that they tend to be rendered entirely useless or experience a significant decrease in efficiency within a short period of time as a result of the interstices in the cellular surfaces becoming filled with debris.